The present invention relates to composite particles, a process for producing the composite particles, and a pigment, paint and resin composition using the composite particles. More particularly, the present invention relates to composite particles which are substantially free from desorption of an organic pigment from the surface thereof and contain no harmful element, a process for producing the composite particles, and a pigment, paint and resin composition using such composite particles.
As well known in the arts, inorganic pigments and organic pigments have been used as colorants for resins, paints, printing inks or the like according to applications thereof. Also, it is known that the inorganic pigments are usually excellent in light resistance, but are deteriorated in tinting strength, thereby failing to show a clear hue. Although some inorganic pigments exhibit a clear hue, many of such pigments contain as essential component, harmful metals such as lead, mercury, cadmium, chromium or the like. Therefore, it has been strongly required to replace these conventional inorganic pigments with alternate materials capable of showing a clear hue, from the standpoints of hygiene, safety and environmental protection.
On the other hand, it is known that the organic pigments usually show a clear hue, but are deteriorated in hiding power and light resistance.
Hitherto, in order to obtain pigments exhibiting excellent properties required for colorants, it has been attempted to combine the inorganic pigments with the organic pigments. For example, there have been proposed the method of co-precipitating chrome yellow and phthalocyanine blue together, the method of adhering an organic pigment to the surface of inorganic pigment particles (Japanese Patent Application Laid-Open (KOKAI) Nos. 4-132770(1992) and 11-181329(1999), etc.) or the like.
At present, it has been strongly required to provide composite particles which are substantially free from desorption of organic pigment from the surface thereof, and contain no harmful elements. However, such composite particles have not been obtained.
That is, in the above method in which chrome yellow and phthalocyanine blue are co-precipitated together, the chrome yellow used therein shows a toxicity, and the obtained pigment shows an insufficient storage stability in a paint produced therefrom due to the co-precipitation production method thereof. Further, when such paint is formed into a coating film, undesired floating tends to be caused thereon.
Also, in the method described in Japanese Patent Application Laid-Open (KOKAI) No. 4-132770(1992), since the organic pigment is simply precipitated in the presence of the inorganic pigment, the adhesion strength of the organic pigment onto the inorganic pigment is insufficient.
Further, in the method described in Japanese Patent Application Laid-Open (KOKAI) No. 11-181329(1999), organopolysiloxane is dissolved in cyclic silicone, and organic pigment particles are added to the resultant solution so as to produce fine particles of the organic pigment. The mixture is impregnated into a high-oil absorptive inorganic pigment. Then, the cyclic silicone is evaporated from the obtained pigment. Therefore, the adhesion strength of the organic pigment onto the inorganic pigment is also insufficient.
Meanwhile, in Japanese Patent Application Laid-Open (KOKAI) No. 11-323174(1999), there are also described black iron-based composite particles comprising as core particles black iron oxide particles or black iron oxide hydroxide particles, a coating layer formed on surface of the core particle which comprises organosilane compounds obtainable from alkoxysilanes, and a carbon black coat formed onto the surface of the coating layer. However, the invention of this KOKAI relates to fixing carbon black onto the black inorganic particles as core particles, and the technique described therein, therefore, is quite different from techniques for obtaining an organic pigment having an excellent hue.
As a result of the present inventors' earnest studies, it has been found that by forming a gluing agent coating layer on surface of a white inorganic particle and forming an organic pigment coat on the gluing agent coating layer in an amount of 1 to 500 parts by weight based on 100 parts by weight of the white inorganic particles, the obtained composite particles having an average particle size of 0.001 to 10.0 μm are substantially free from desorption of organic pigment from the surface thereof, and are usable as a harmless pigment. The present invention has been attained on the basis of the finding.